1. Field of the Invention
The present invention is broadly concerned with an improved magnetic switch assembly of the type used in conjunction with a security system to detect unauthorized entry through doors or windows. More particularly, it is concerned with such a switch assembly which is especially configured to defeat attempted magnetic manipulation of the switch assembly so as to permit opening of the door or window without detection thereof. To this end, the switch assembly includes a pair of adjacent, upper and lower switch elements mountable within a stationary frame, with a shiftable ferromagnetic body disposed between the elements and movable between spaced upper and lower switch operating positions; a magnet is mounted in the movable door or window and is oriented for effecting movement of the body upon opening of the door or window between switch operating positions. In the event that an external magnet is placed adjacent the switch elements during an attempted unauthorized entry, the ferromagnetic body is moved to the lower switch position, thereby detecting such attempted manipulation.
2. Description of the Prior Art
Modern-day building security alarm systems make use of door and window switch assemblies which are designed to detect unauthorized opening thereof. For example, one common switch assembly for this purpose includes a pair of magnetic reed switch elements mounted in a door or window frame, with a magnet carried by the adjacent openable door or window. The magnet carried by the door or window hold the reed elements opened or closed (depending on whether the switch is of the normally opened or normally closed variety) when the door or window is closed; when the latter is opened, the reed switch elements change position. These reed switches are conventionally interposed in the overall alarm circuit, so that upon unauthorized opening of the door or window, the switch operation generates an alarm signal.
One problem with conventional reed switch assemblies of the type described is that they can be readily defeated by simply placing an external magnet adjacent the door or window frame in proximity to the reed switch elements. This allows the door or window to be opened, but the reed switches do not change their positions, owing to the presence of the magnetic field attendant to the external magnet. As a consequence, an intruder may with impunity open the door or window and gain unauthorized access to the seemingly protected building.
There is accordingly a real and unsatisfied need in the art for an improved switch assembly which is designed to defeat attempted magnetic manipulation thereof, and to initiate alarm operation even when an external magnet is employed.